You must not sell a lot. I get the "oh, I didn't realize Buy It Now means I bought it" excuse a lot. eBay instituted a secondary screen explaining that bidding is entering into a contract for a reason. I still get complaints when I sell, everything from "oh, I entered the wrong price" to "oh, I didn't read the item description".
The point is when he clicked that buy button he entered into a contract. The one-click aspect is just his way of trying to weasel out of it.
